1. Field of the Invention
The present invention relates to a damper mechanism for use in an automotive air-conditioner, which includes a film-like damper having air vents defined therein and opposite ends wound around first and second takeup shafts, respectively.
2. Description of the Related Art
Air-conditioners for use on motor vehicles such as automobiles comprise a blower unit, a cooler unit, an a heater unit. Such air-conditioners have an air-mixing damper for mixing hot air and cold air to determine the temperature of air to be introduced into a passenger's compartment and a mode-selecting damper for selecting one of air flow modes "VENT", "FOOT", and "DEF".
Those dampers have conventionally comprised plate-like dampers. However, damper mechanisms comprising film-like dampers have recently been used instead of plate-like dampers. One conventional damper mechanism comprising film-like dampers is shown in FIG. 23 of the accompanying drawings. As shown in FIG. 23, a film-like air-mixing damper 3 has opposite ends wound around drive and driven shafts 1, 2 which serve as takeup shafts, and also has a plurality of air vents 4 defined therein at a given position and extending over a predetermined length. The drive shaft 1 has an end fixed to a drive pulley 5 which is connected to the shaft of a stepping motor 6. The driven shaft 2 supports on one end thereof a driven pulley 7 on which a tension spring (not shown) acts. A wire 8 is trained around the drive pulley 5 and the driven pulley 7.
A film-like mode-selection damper 9 is similar in structure to the film-like air-mixing damper 3. Those parts of the film-like mode-selection damper 9 which are identical to those of the film-like air-mixing damper 3 are denoted by identical reference numerals, and will not be described in detail.
When the stepping motor 6 is energized, the drive shaft 1 is rotated in unison with the drive pulley 5 in one direction, winding or unreeling the film-like air-mixing damper 3. At the same time, the driven shaft 2 is rotated by the driven pulley 7 which is rotated by the wire 8, unreeling or winding the film-like air-mixing damper 3. The film-like air-mixing damper 3 is thus moved until the air vents 4 in the film-like air-mixing damper 3 reach a desired position. The air vents 4 thus positioned varies the ratio at which hot air and cold air are mixed, thereby adjusting the temperature of air introduced into the passenger's compartment.
When the driven shaft 2 winds up the film-like air-mixing damper 3 by rotation of the drive shaft 1, since the diameter of the roll of the film-like air-mixing damper 3 wound on the driven shaft 2 progressively increases, the angular displacement of the driven shaft 2 becomes smaller than the angular displacement of the drive shaft 1. Conversely, when the drive shaft 1 winds up the film-like air-mixing damper 3, since the diameter of the roll of the film-like air-mixing damper 3 wound on the drive shaft 1 progressively increases, the angular displacement of the driven shaft 2 becomes greater than the angular displacement of the drive shaft 1, resulting in a torque variation. To absorb such a torque variation, the stepping motor 6 is required to be of a large size capable of generating a torque sufficiently greater than a minimum drive torque which is necessary to rotate the drive and driven shafts 1, 2. Furthermore, a process of controlling the stepping motor 6 is considerably complex in order to position the air vents 4 in an accurate location for desired temperature adjustment.